1. Technical Field
The present invention relates to an ultrasonic device, an ultrasonic module, and an ultrasonic measurement apparatus.
2. Related Art
In the related art, there is a piezoelectric device including a vibration film and a piezoelectric element as a vibrator causing the vibration film to vibrate, provided on the vibration film (for example, JP-A-2015-195351). The piezoelectric device transmits an ultrasonic wave by driving the piezoelectric element and causing the vibration film to vibrate, and receives an ultrasonic wave by detecting vibration of the vibration film caused by the ultrasonic wave with the piezoelectric element.
The piezoelectric device disclosed in JP-A-2015-195351 further includes an acoustic matching layer provided on the vibration film, and an acoustic lens which is provided on the acoustic matching layer and has acoustic impedance similar to that of a living body as a measurement target. The piezoelectric device transmits and receives ultrasonic waves in a state in which the acoustic lens is brought into contact with a measurement target such as a living body. For example, an ultrasonic wave transmitted through driving of the piezoelectric element propagates through the acoustic matching layer and the acoustic lens, and is then output into a living body from a surface of the acoustic lens.
Here, as described above, in the configuration in which the acoustic matching layer and the acoustic lens are laminated, there is a case where some ultrasonic waves (hereinafter, also referred to as first waves) transmitted from the vibrator are output to a measurement target from the acoustic lens, and other ultrasonic waves are reflected at an interface between the acoustic matching layer and the acoustic lens. In this case, interface reflected waves which are reflected at the interface are reflected toward the acoustic lens side in the vibrator, and are output to the living body from the acoustic lens, and thus there is concern that a distance resolution may be reduced.
In other words, the interface reflected waves are delayed by the time corresponding to a thickness of the acoustic matching layer with respect to the first waves, and are then emitted to the measurement target. Thus, the first waves reflected from the measurement target and the interface reflected waves reflected from the measurement target are detected at different timings. In this case, there is a problem in that so-called tailing occurs in which not only a peak corresponding to the first waves but also a peak corresponding to the interface reflected waves is detected in a received signal which is output when the piezoelectric device receives the ultrasonic waves, and thus a distance resolution is reduced.